Fire detector made with photodiode ----- Fire Detection

This is an ultra-sensitive fire detector that uses a photodiode as a fire sensor. Once the spark or fire is detected, the fire detector will immediately issue a alarm and immediately cut off the power supply. The drawings are fire detector circuits. The voltage generated by the photodiode in the infrared detector is proportional to the incident light or infrared light falling above it, and since this voltage is small, it is necessary to push the remainder of the circuit with a high-digit voltage amplifier. In the figure, the dual transport chip 741 (IC1) is used as a Schmidt trigger with a hysteresis effect. It transforms the output signal of the photodiode to a pulse signal having a certain waveform. The R1 and R2 constitute a voltage drop to the inverted input feet 2 to which the power supply voltage is sent to the IC1, and R3 is feedback the output feedback to the feedback resistance of the inverted input foot. The photodiode D1 is coupled between the nodes of the voltage divider R1, R2 and the same phase input sheet 3 of IC1. When there is no light, the voltage of both ends of the photodiode is zero. At this time, the output of IC1 is a low potential. When spark or fire suddenly occurs, the photodiode is turned on, the IC1 output is high, and the high potential can remain a few seconds even after the photodiode is turned off. The high potential of IC1 is not affected by slight changes in the inverted input foot potential. So this is conducive to the trigger of the alarm circuit. The high potential of IC1 is used to trigger the HSBT169 (SCR1) to promote the relay RL1. After the absorption, the fire appliance is immediately disconnected by the relay contact. The SCR1 remains in the latch until the switch S1 is pressed (disconnected). Further, after the SCR1 is turned on, the transistor T1 base obtains a bias voltage, and the alarm acoustic generator chip UM3562 (IC2) is activated, while the regulator diode ZD1 causes the supply voltage of IC2 to be secure 3.1V. Getting the 6 foot of IC2, allowing IC2 to issue a fire alarm. The output of the IC2 is amplified by T2 to make the speaker LS1 alert. The photodiode is connected to the electrical diode with a single-shielded wire and placed it in a power supply portion close to the electrical appliance. To avoid false triggers, the photodiode should be placed in the least light of direct light.

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